It is known in the art to use heat treatable aluminum alloys in a number of applications involving relatively high strength such as aircraft fuselages, vehicular members and other applications. Aluminum alloys 6061 and 6063 are well known heat-treatable aluminum alloys. These alloys have useful strength and toughness properties in both T4 and T6 tempers. As is known, a T4 condition refers to a solution heat treated and quenched condition naturally aged to a substantially stable property level, whereas a T6 temper refers to a stronger condition produced by artificially ageing. These known aluminum alloys lack, however, sufficient strength for most structural aerospace applications.
Several other AA6000 series alloys are generally unsuitable for the design of commercial aircraft which require different sets of properties for different types of structures. Depending on the design criteria for a particular airplane component, even small improvements in strength, fracture toughness and fatigue resistance result in weight savings, which translate to fuel economy over the lifetime of the aircraft, and/or a greater level of safety. To meet these demands several other 6000 series alloys have been developed.
European patent application EP-A-0173632 concerns extruded or forged products of an alloy consisting of the following alloying elements, in wt. %:
Si 0.9–1.3, preferably 1.0–1.15Mg 0.7–1.1, preferably 0.8–1.0Cu 0.3–1.1, preferably 0.8–1.0Mn 0.5–0.7Zr0.07–0.2, preferably 0.08–0.12Fe<0.30Zn 0.1–0.7, preferably 0.3–0.6                balance aluminum and unavoidable impurities (each <0.05, total <0.15).The products have a non-recrystallised microstructure. This aluminum alloy has been registered under the AA designation 6056.        
European patent application EP-A-0173632 concerns extruded or forged products of an alloy consisting of the following alloying elements, in wt. %:
It has been reported by that this known AA6056 alloy is sensitive to intercrystalline corrosion in the T6 temper condition. In order to overcome this problem U.S. Pat. No. 5,858,134 provides a process for the production of rolled or extruded products having the following composition, in wt. %:
Si0.7–1.3Mg0.6–1.1Cu0.5–1.1Mn0.3–0.8Zr<0.20Fe<0.30Zn<1Ag<1Cr<0.25                other elements <0.05, total <0.15        balance aluminum,and whereby the products are brought in an over-aged temper condition requiring time and money consuming processing times at the end of the manufacturer of aerospace components. In order to obtain the improved intercrystalline corrosion resistance it is essential for this process that in the aluminum alloy the Mg/Si ratio is less than 1.        
U.S. Pat. No. 4,589,932 discloses an aluminum wrought alloy product for e.g. automotive and aerospace constructions, which alloy was subsequently registered under the AA designation 6013, having the following composition, in wt. %:
Si0.4–1.2, preferably 0.6–1.0Mg0.5–1.3, preferably 0.7–1.2Cu0.6–1.1Mn0.1–1.0, preferably 0.2–0.8Fe<0.6Cr<0.10Ti<0.10                the balance aluminum and unavoidable impurities.The aluminum alloy has the mandatory proviso that [Si+0.1]<Mg<[Si+0.4], and has been solution heat treated at a temperature in a range of 549 to 582° C. and approaching the solidus temperature of the alloy. In the examples illustrating the patent the ratio Mg/Si is always more than 1.        
U.S. Pat. No. 5,888,320 discloses a method of producing an aluminum alloy product. The alloy product has a composition of, in wt. %.:
Si0.6–1.4, preferably 0.7–1.0Fe<0.5, preferably < 0.3Cu<0.6, preferably < 0.5Mg0.6–1.4, preferably 0.8–1.1Zn0.4 to 1.4, preferably 0.5–0.8                at least one element selected from the group:                    Mn 0.2–0.8, preferably 0.3–0.5            Cr 0.05–0.3, preferably 0.1–0.2                        balance aluminum and unavoidable impurities.The disclosed aluminum alloy provides an alternative for the known high-copper containing 6013 alloy, and whereby a low-copper level is present in the alloy and the zinc level has been increased to above 0.4 wt. % and which is preferably in a range of 0.5 to 0.8 wt. %. The higher zinc content is reported to be required to compensate for the loss of copper.        
European patent application EP-1143027 discloses a method for producing an Al—Mg—Si alloy of the 6000 series having a composition of, in wt. %:
Si0.7–1.3Mg0.6–1.1Cu0.5–1.1Mn0.3–0.8Zn<1Fe<0.3Zr<0.2Cr<0.25                other elements <0.05, total <0.15        balance aluminum,wherein the products are subjected to an artificial ageing procedure to improve the alloy and to meet high damage tolerance (“HDT”) characteristics similar to those of the AA2024 series which are preferably used for aeronautical applications but which are not weldable. The ageing procedure is optimized by using a respective function of the chemistry.        
European patent application EP-1170118-A1 discloses an aluminum alloy similar to the one described in EP-1143027 wherein an aluminum alloy sheet for aeronautical applications is clad on one or both surfaces in order to improve the corrosion resistance. The core sheet in AA6000 series alloy is clad with a cladding sheet in an alloy of Al—Zn type. Those clad sheets, which may be used to manufacturer aircraft structural parts, do have the advantage that they are resistant to corrosion and have improved static mechanical properties. It is also described to homogenize the core material before applying the cladding within a temperature range of between 530° C. and 575° C. for a period of between 1 and 8 hours.
U.S. Pat. No. 5,607,524 discloses a method for making an aluminum drive shaft for automobiles or trucks from aluminum alloy tube. The aluminum alloy covers a very broad range of 6000-series alloys. The tube is being made by extrusion within a temperature range of about 260 to 426° C.
EP-1029937-A1 discloses an Al—Mg—Si alloy sheet with improved press-formability over conventional Al—Mg—Si based alloy sheets by controlling the orientation density of at least the Cube orientation. The material is suitable for an engine hood or trunk hood of an automobile.
Even though the alloys of the AA6000 series have the general advantage of being weldable the high copper content, however, is detrimental with regard to the corrosion resistance even though copper enhances the strength of the aluminum alloy. Especially for designing structural parts for aeronautical applications improvements in fatigue crack growth resistance and low amount of intermetallics result in better properties and in weight savings which translate to fuel economy over the lifetime of the aircraft or to a greater level of safety.